Question: Which of these numbers is prime? ${15,\ 27,\ 37,\ 46,\ 49}$
A prime number has exactly two factors: 1 and itself. The factors of 15 are 1, 3, 5, and 15. The factors of 27 are 1, 3, 9, and 27. The factors of 37 are 1 and 37. The factors of 46 are 1, 2, 23, and 46. The factors of 49 are 1, 7, and 49. Thus, 37 is a prime number.